Re: [PATCH v1 1/5] PCI: Don't suspend IOMMU when probing reset capability

[Bjorn Helgaas <helgaas@kernel.org>]

On Tue, Nov 03, 2026 at 10:33:42AM -0800, Nicolin Chen wrote:
> reset_method_store() in drivers/pci/pci-sysfs.c discovers supported reset
> methods by calling reset_fn(pdev, PCI_RESET_PROBE, ...) without holding a
> device_lock, since the probe path is expected to query the device's reset
> capability without changing device state.
> 
> However, pci_reset_bus_function() and __pci_dev_specific_reset() violate
> that contract after pci_dev_reset_iommu_prepare/done() were added, which
> moves the device into a blocking domain and abruptly aborts any in-flight
> DMA. Doing this for a probe -- a state-query call that does not even hold
> device_lock -- can cause driver timeouts and data loss on a DMAing device.
> 
> The peer reset helpers all handle this correctly: they short-circuit on a
> probe input before touching the IOMMU.
> 
> Skip pci_dev_reset_iommu_prepare()/_done() entirely when probe is set. The
> inner reset routines already implement their own probe semantics, and they
> perform the capability checks and return without changing device state.
> 
> Fixes: f5b16b802174 ("PCI: Suspend iommu function prior to resetting a device")
> Cc: stable@vger.kernel.org
> Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>

Acked-by: Bjorn Helgaas <bhelgaas@google.com>

> ---
>  drivers/pci/pci.c    | 13 ++++++++-----
>  drivers/pci/quirks.c | 13 ++++++++-----
>  2 files changed, 16 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 7c6f2aba81443..38b680e7c3d60 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -5042,10 +5042,12 @@ static int pci_reset_bus_function(struct pci_dev *dev, bool probe)
>  	if (bridge && pcie_is_cxl(bridge) && cxl_sbr_masked(bridge))
>  		return -ENOTTY;
>  
> -	rc = pci_dev_reset_iommu_prepare(dev);
> -	if (rc) {
> -		pci_err(dev, "failed to stop IOMMU for a PCI reset: %d\n", rc);
> -		return rc;
> +	if (!probe) {
> +		rc = pci_dev_reset_iommu_prepare(dev);
> +		if (rc) {
> +			pci_err(dev, "failed to stop IOMMU for a PCI reset: %d\n", rc);
> +			return rc;
> +		}
>  	}
>  
>  	rc = pci_dev_reset_slot_function(dev, probe);
> @@ -5054,7 +5056,8 @@ static int pci_reset_bus_function(struct pci_dev *dev, bool probe)
>  
>  	rc = pci_parent_bus_reset(dev, probe);
>  done:
> -	pci_dev_reset_iommu_done(dev);
> +	if (!probe)
> +		pci_dev_reset_iommu_done(dev);
>  	return rc;
>  }
>  
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 7f1f47ea2ee41..3d3e95cb9f7dc 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -4406,14 +4406,17 @@ static int __pci_dev_specific_reset(struct pci_dev *dev, bool probe,
>  {
>  	int ret;
>  
> -	ret = pci_dev_reset_iommu_prepare(dev);
> -	if (ret) {
> -		pci_err(dev, "failed to stop IOMMU for a PCI reset: %d\n", ret);
> -		return ret;
> +	if (!probe) {
> +		ret = pci_dev_reset_iommu_prepare(dev);
> +		if (ret) {
> +			pci_err(dev, "failed to stop IOMMU for a PCI reset: %d\n", ret);
> +			return ret;
> +		}
>  	}
>  
>  	ret = i->reset(dev, probe);
> -	pci_dev_reset_iommu_done(dev);
> +	if (!probe)
> +		pci_dev_reset_iommu_done(dev);
>  	return ret;
>  }
>  
> -- 
> 2.43.0
>